Anonymous wrote:what is "happy tail"? does your dog chew his tail when he's happy??
http://www.canidae.com/blog/2012/07/what-is-happy-tail-syndrome-in-dogs.html
We had a coonhound that used to have this problem when we first adopted him. Luckily it was related to crating, so we were able to stop crating quickly and it healed up fine. But we had several occasions where he left a nice dog height trail of blood around the house because he was doing his "I'm so glad you're home" sprints around the house while bleeding. It's so sad when they hurt themselves because they're happy! Good luck OP (and PP).